Chapter 16, Problem 18P

Seven E. coli mutants were isolated. The activity of the enzyme β-galactosidase produced by cells containing each mutation alone or in combination with other mutations was measured when the cells were grown in medium with different carbon sources.

Assume that each of the seven mutations is one and only one of the genetic lesions in the following list. Identify the type of alteration each mutation represents.

a. superrepressor

b. operator deletion

c. nonsense (amber) suppressor tRNA gene (assume that the suppressor tRNA is 100% efficient in suppressing amber mutations)

d. defective CRP–cAMP binding site

e. nonsense (amber) mutation in the β-galactosidase gene

f. nonsense (amber) mutation in the repressor geneg. defective crp gene (encoding the CRP protein)

g. defective crp gene (encoding the CRP protein)